Ingest OTLP traces for a run (monitor-URL form)

The alternative to the Bearer form above, for an exporter that cannot set headers: the URL's monitor_id names the check and its project directly — the monitor id in the URL is itself the capability, exactly like a ping URL. No Authorization header is required.

A lastping.monitor_id resource attribute is still allowed, but only to REPEAT the URL's id — never to override it; a mismatch is 400. lastping.run_id is optional, exactly as on the Bearer form: without it each trace becomes its own run. The request is subject to every cap and the same 3,600-requests/hour/project bucket the Bearer form uses.

A Bearer header MAY additionally be sent on this form; if present, it must be a valid key belonging to this monitor's own project (403 otherwise, not 404 — the URL already proves the monitor exists, so unlike the Bearer-only form there is no existence oracle to protect here). A key bound to a different monitor is 400.

Secrets are redacted and the daily span budget applies exactly as on the Bearer form.